The Elder Scrolls series is currently celebrating its 25th anniversary, and in order to get everyone into the festive mood, Bethesda is currently offering a free copy of the truly excellent The Elder Scrolls: Morrowind. You will have to be quick, however, as the offer will only be available throughout March.
As for the whole process, it's a pretty simple one. You'll need to create or log into your Bethesda account over at the official website, after which you'll need to redeem the code TES25TH-MORROWIND to receive your free copy of Morrowind. That's pretty much it!
If you're wondering whether it's actually worth playing Morrowind despite its age, I would say the answer is a resounding yes if you're a fan of RPGs. It may be a bit clunky and its combat is nothing to write home about, but the world is so unique and so filled with interesting characters that you won't really care about that after a while.
That said, before you begin your playthrough, I would highly advise installing a couple of mods to make the whole experience more interesting. There are numerous community packs out there, so simply do a bit of research to see which one fits your playstyle and you'll have a much better experience with Morrowind because of it.
Have fun!